Standard O-ring sizes are defined by two core dimensions: inner diameter (d₁) and cross-section diameter (d₂, wire diameter). All major standards follow these two key parameters, together with matching tolerances and standardized series rules. The sizing principles and common standards are as follows:
1. Core Dimension Standards: All standards first establish a standard series for the cross-sectional diameter d2 (wire diameter) (e.g., 1.8, 2.4, 3.1, 5.7, 7.0 mm, etc.), and then match the wire diameter with standardized values for the inner diameter d1. Furthermore, d1 increases in fixed increments to avoid a chaotic array of specifications.
2. Dimensioning Rules: The general notation is d1×d2 (inner diameter × wire diameter). In some cases, the outer diameter (d1+2×d2) may be specified, but the standard core remains based on d1 and d2;
3. Tolerance Specifications: Different standards define upper and lower deviations for d1 and d2 based on size ranges (e.g., small inner diameter/large inner diameter, fine wire diameter/coarse wire diameter) to ensure interchangeability.
Main Common Standards (Most Widely Used in Industry)：
– GB/T 3452.1 (Chinese National Standard)
The mainstream standard in China. It defines a narrow series (1.0–4.0 mm) and a wide series (5.7–12.0 mm) for crosssection diameters. Inner diameters are matched to each crosssection, covering most general industrial applications.
– AS568 (American Standard)
Widely used globally, especially in hydraulic and pneumatic systems. Each part number corresponds to a unique d₁×d₂ size (e.g., AS568010 = 1.78 × 1.78 mm). Key crosssections include 1.78, 2.62, 3.53, and 5.33 mm, widely compatible with American and European equipment.
– JIS B 2401 (Japanese Standard)
Divided into Type P (general) and Type G (precision). Its crosssection and inner diameter series differ slightly from GB and AS568, mainly for Japanese machinery.
– ISO 3601 (International Standard)
Highly aligned with GB/T 3452.1, serving as the unified global basic specification with consistent core dimension series.
Key Notes:
Standards clearly specify the matching rules for minimum groove dimensions. The Oring inner diameter d₁ and crosssection d₂ must be compatible with the bore and width of the installation groove (typical compression ratio: 10%–20%).
This is also a necessary design requirement supporting size standardization.
